Water was "somewhere between ankle and hip deep."

The science team behind the Mars Curiosity rover has announced that some of the images it has taken reveal signs of a significant water flow at some point in the planet's past. Although there have been numerous indications of water in Mars' past, the discovery provides a unique opportunity to understand the precise environment in which the watery deposits formed.

The deposits look strikingly similar to some found on Earth, in which rounded rocks, carried by currents, settle into a stream bed and are locked into a conglomerate. The rounded shapes show that the rocks were worn by transport over long distances, while the size of the rocks is too large for them to have been brought there by wind. The flows seem to have been sizable, too. "From the size of gravels it carried, we can interpret the water was moving about 3 feet per second, with a depth somewhere between ankle and hip deep," said Berkeley's William Dietrich in the JPL's release.

The Gale Crater, where Curiosity landed, shows signs of extensive water flows, with a channel that leads to a break in the crater rim, and a large alluvial fan within the crater itself. The size of these features suggest that the flow was either steady, or recurred repeatedly.

Since the rocks embedded in the conglomerate were carried from above the rim, examining them with some of the rover's instruments should provide some indication of the region's geology, and the deposits in which they are embedded will tell us something about the watery conditions. But the fact that they were found in more than one location already suggests that Curiosity will come across more before too long.

JPL's statement quotes Caltech's John Grotzinger as saying the deposits are probably not a good bet for finding any organic material that might be indicative of anything living in the water. But they hope to find any organic deposits that are present preserved at Mount Sharp, the largest feature in the crater. These further indications of water, Grotzinger says, are "insurance that we have already found our first potentially habitable environment."

Mars cooled much sooner than earth (it's less massive, in fact it only has about 11% the mass of earth it's also less dense) and as such lost or never had the liquid iron dynamo at it's core that earth does generating a strong magnetic field. Without the magnetic field to protect it, and with less mass / gravity, over time the solar winds blew away the early martian atmosphere, likely deposited by objects from the outer solar system during the late heavy bombardment. Without an atmosphere to conduct heat, the temperature differential between the poles and the equator increased. Any liquids closer to the equator and close to or on the surface probably sublimated, while liquids underground froze. The liquids at the poles froze. So now you have liquid trapped at the poles and the sub surface, with no atmosphere or significant weather to bring surface liquid back to the warmer areas near the equator.

Mars cooled much sooner than earth (it's less massive, in fact it only has about 11% the mass of earth it's also less dense) and as such lost or never had the liquid iron dynamo at it's core that earth does generating a strong magnetic field. Without the magnetic field to protect it, and with less mass / gravity, over time the solar winds blew away the early martian atmosphere, likely deposited by objects from the outer solar system during the late heavy bombardment. Without an atmosphere to conduct heat, the temperature differential between the poles and the equator increased. Any liquids closer to the equator and close to or on the surface probably sublimated, while liquids underground froze. The liquids at the poles froze. So now you have liquid trapped at the poles and the sub surface, with no atmosphere or significant weather to bring surface liquid back to the warmer areas near the equator.

Mars cooled much sooner than earth (it's less massive, in fact it only has about 11% the mass of earth it's also less dense) and as such lost or never had the liquid iron dynamo at it's core that earth does generating a strong magnetic field. Without the magnetic field to protect it, and with less mass / gravity, over time the solar winds blew away the early martian atmosphere, likely deposited by objects from the outer solar system during the late heavy bombardment. Without an atmosphere to conduct heat, the temperature differential between the poles and the equator increased. Any liquids closer to the equator and close to or on the surface probably sublimated, while liquids underground froze. The liquids at the poles froze. So now you have liquid trapped at the poles and the sub surface, with no atmosphere or significant weather to bring surface liquid back to the warmer areas near the equator.

-kap

You may not be a professional, but you sure sound like one. That's a pretty damned good and reasonable guess as well.

I think everyone is jumping the gun to claim flowing water. Look at the material in cross-section... it is obviously just some chunks of concrete left behind by an advanced civilization which has since left Mars for interstellar space.

The real surprise is that we're seeing this so far from the rim. Curiosity landed almost at the edge of the alluvial fan since the aim was to get close to Mt. Sharp, which is the primary mission objective. Before the landing speculation was that we might find ancient clay beds (transformed into shale or slate when the crater floor was buried) since all the larger material would have been deposited further upstream.

All I can say is - Wow! If we're seeing embedded rocks on the order of 1cm at this point it suggests that the amount of water present far exceeded expectations.

The thing about flowing water implies other interesting criteria, like temperature and air pressure. For water to flow, temp had to be above the freezing point and below boiling. It also suggests that the air pressure was sufficient to keep the water from vaporizing away. This is a big puzzle. Learning why the water went away could tell us much about planetary evolution cycles.

@Ars: Could you make a dedicated astronomy section (haven't found on yet).@Everybody else: Do you know some good, if possible "simply" written astronomy news sites? I'm really fascinated by this stuff, but don't have the education (yet) too fully understand scientific stuff. Nonetheless, I'm trying

Is Mars a "dead earth"? Will we be able to terraform it to our purposes? I'm getting really glad that I live in this age.. These discoveries are amazing! And thanks to the internet, we have access to the information from nearly everywhere!

How do they know it was water. Could it have been some other liquid substance?

like co2? the caps are dry ice... but I don't know if co2 has a liquid state? /not a chemist

Well, since you mention it ... Yes, one person has suggested a theory in which certain features seen on Mars could have been caused by CO2 under pressure and in a liquid state - specifically the outburst floods. There used to be more about this at Nick Hoffman's website, but it's returning a 404 right now.

There are lots of features that this theory can't explain, though, since many of them require fluid to be present on the surface (and thus at too low a pressure for CO2 to be a liquid). It's generally accepted that H2O is the only substance that can explain everything we've seen so far on Mars.

"Dad are you space?""Yes, now we are a family again.""Oh play it cool play it cool here come the space cops. Space court. Judge Space Presiding. GUILTY! OF BEING IN SPACE!""Hey. Hey. Hey lady. Hey. Space."

@Ars: Could you make a dedicated astronomy section (haven't found on yet).

If you look just below the title, you should see two red tabs, one of which is labelled "Space". Click that, and you'll be taken to a page with all our stories that fit under that rough heading. You'll get some basic space business, and will miss out on a lot of good science, but if you just want a quick skim of that content, it's a convenient way to go.